Pressure switch



Dec. 4, 1956 E. SAUER 2,773,146

PRESSURE SWITCH Filed Nov. 25, 1954 26 2s Fig.|.

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o Fig.2. F|g.3. 64 w B INVENTOR 70 "5 g 65 United States Patent PRESSURESWITCH Louis E. Sauer, Sharon, Pa., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa, :1 corporation of PennsylvaniaApplication November 23, 1954, Serial No. 470,639

3 Claims. (Cl. 20083) This invention relates to relays and, inparticular, to pressure and/or rate of pressure change responsive relaysfor efiecting the disconnection of a transformer from a power sourcewhen a fault occurs within the transformer.

When a fault occurs within the transformer, such as to produce an arebetween the transformer windings, a disintegration of the insulatingmaterial and oil disposed around the winding takes place. Such arcs,having once started, are likely to continue until the disintegration ofthe insulation reaches such a point that the current to the windingbecomes of sufficient magnitude to trip a line breaker and disconnectthe transformer from the power source. However, it is a considerableperiod of time from the initiation of the fault to that time when theline breaker is tripped. Due to the fact that the arc is permitted tocontinue during this time interval, considerable damage may be done tothe transformer windings. it is, therefore, desirable to disconnect thetransformer from the power source during the early stages of the faultregardless of its magnitude.

An object of this invention is to provide a new and improved relay thatis responsive to two operating conditions.

Another object of this invention is to provide a pressure responsiverelay which effects an operation in re sponse to both a sudden increasein pressure and to a predetermined pressure, but not to gradualincreases in pressure.

A further object of this invention is to provide for increasing thespeed of response of a pressure responsive relay.

Still another object of this invention is to provide a pressureresponsive relay which has a high speed of response and yet a minimum ofmaintenance.

Another object of this invention is to provide a pres sure responsiverelay which is so constructed and associated with a transformer tankthat normal movement of the transformer tank wall, due to changes inpressure within the tank, has substantially no adverse effect on theoperation of the pressure responsive relay.

A more specific object of this invention is to provide for soassociating a pivoted arm member having a switch mounted thereon withpressure responsive means and with a stop member that the inertia of thepivoted arm mem' ber prevents its movement on sudden pressure changes tothus effect an actuation of the switch, and yet permits bodily movementof the switch in response to gradual changes in pressure until the stopmember prevents its further movement and thus permits the pressureresponsive means to effect an actuation of the switch.

Other objects of this invention will become apparent from the followingdescription when taken in conjunction with the accompanying drawing, inwhich:

Fig. 1 is a schematic diagram of a transformer embodying the teachingsof this invention;

Fig. 2 is a view partly in section taken along the line Ii-ll of Fig. 1;and

2,773,146 Patented Dec. 4, 1956 Fig. 3 is a detail view of themicroswitch shown in Fig. 1 with cover off.

Referring to Fig. 1, this invention is illustrated by reference to atransformer 10. As is customary, the transformer 10 comprises areceptacle or transformer tank 12 within which is disposed a magneticcore member 14 having primary windings 16 and 17 disposed in inductiverelationship therewith. In this instance, the transformer tank 12 is ofthe form-fit type, however, it is to be understood that other types ofreceptacles or tanks are equally applicable to this invention. In orderto electrically insulate the various components such as the core member14 and the windings 16 and 17 from one another and from the tank 12, adielectric fluid, such as transformer oil 18, is disposed in the tank12.

Under normal operating conditions the pressure within the tank 12 mayincrease gradually due to for instance changes in ambient temperature orchanges in the load on the transformer. This effects an increase in thetotal pressure within the tank 12. However, a fault produces impulsechanges in pressure of varying magnitude, but does not materially effectthe total pressure within the tank 12.

In accordance with the teachings of this invention, a protective deviceor pressure responsive relay 20 is provided to effect a deenergizationof the transformer Iii when the pressure of the transformer oil 18suddenly increases, or when the pressure of the transformer oil 18increases to a predetermined value under normal operating conditions.However, as will be explained more fully hereinafter, the pressureresponsive relay 21) does not immediately effect a deenergization of thetransformer 10 when gradual increases in the magnitude of the pressureof the transformer oil 18 occur. Thus, the transformer 16 is protectedfrom faults of large or small magnitude and from gradual increases inpressure which continue for a relatively long period of time so as toincrease the transformer oil pressure to a predetermined value.

Deenergization of the transformer 10 is effected by a circuit breaker 22which is responsive to the operation of the pressure responsive relay20. The circuit breaker 22 is shown schematically and comprises movableand stationary contact members 24- and 26, respectively, a tripmechanism 28, and a handle 29 for effecting a manual resetting of thecircuit breaker 22. As shown, the trip mechanism 28 includes a magneticcore member 30, the positioning of which is determined by theenergization of an operating coil 32. In order to effect a return of themagnetic core member 30 to its normal position after having beenactuated as a result of current flow through the operating coil 32, acompression spring 34 is provided.

Energy for the transformer 10 i received from a power source (not shown)through supply conductors 36 and 38 which are connected to the primarywindings 16 through high voltage bushings 40. On the other hand, thesecondary winding 17 is connected to a load (not shown) through lowvoltage bushings 42.

Broadly, the pressure responsive relay 20 comprises pressure responsivemeans 44 responsive to changes in the pressure of the transformer oil18, a movable switch 46 normally biased to a predetermined position bygravity, the pressure responsive means 44 being disposed to effect anactuation of the movable switch 46 in response to sudden changes in thepressure of the transformer oil. and effect a bodily movement of themovable switch 46. without actuating the switch 46, in response togradual changes in the pressure of the transformer oil 18, and a stopmember for limiting the bodily movement of the movable switch 46 so thatthe pressure responsive means 44 can effect an actuation of the movableswitch 46.

Specifically, the pressure responsive means 44 comprises a metallicSylphon bellows Stl having a base member 52. The end opposite the basemember 52 is suitably secured to a plate member 54 which carries an adjusting-nutPSS having a passageway 56 for'receiving an actuating memberor a switch operating rod 56' which is suitably secured to the basemember 52 for movement therewith. As illustrated, the passageway 56 isof such diameter that the interior of the Sylphon bellows 54 is exposedto atmospheric pressure and, thus, owing to a minimum of inertia,quickly responds to a change in the pressure of the transformer oil 18.However, the exterior of the Sylphon bellows 56 is exposed only to thepressure of the transformer oil 18, the transformer tank 12 being sealedoff to atmospheric pressure.

In order to bias .the Sylphon bellows St) to its extended position, acompression spring 60 is disposed around the switch operating rod'Stiand between the adjusting nut 55 and the base member 52 of the Sylphonbellows 56. In practice, the strength of the compression spring 60determines the pressure range over which the pressure responsive relay20 will effectively operate. That is, the higher the expected pressureof the transformer oil 18 at the relay location, the greater must be theresisting force of the compression spring 66. However, in order toadjust for small variations in the magnitude of the static head of oil18, the adjusting nut 55 is provided. As illustrated, the nut 55threadedly engages the plate 54 and bears against the end of thecompression spring 64 The higher the head of oil 18 the further is thenut 55 screwed into the plate 54. Thus, irrespective of the magnitude ofthe head of oil 18, the positioning of the rod 58 with respect to themovable switch 46 is maintained.

As illustrated, the movable switch 46 is mounted for movement with apivoted arm 62 which pivots about a pivot point 64. Also mounted formovement with the pivoted arm 62 is a mass or adjustable nut 65.Specifically, the adjustable nut 65 threadedly engages the end of thepivoted arm 62. Thus, the distance of the nut 65 from the pivot point 64can be readily varied. in order toprevent movement of the adjustable nut65 with respect to the pivoted arm 62 once the desired position of thenut 65 has been obtained, a lock nut 68 is provided.

The pivoted arm 62. the movable switch 46, the adjustable nut 65, andthe lock nut 66 comprise an unbalanced mass whose inertia can be changedby varying the position of the adjustable nut 65 along the length of thepivoted arm 62-. For instance, if the distance between the adjustablenut 65 and the pivot point 64 is decreased, the inertia of theunbalanced mass is likewise decreased, to thereby require a more rapidrate of increase, or a more sudden increase in the pressure of thetransformer oil 318. in order to effect an actuation of the movableswitch 46. Thus, by adjusting the nut 65, the value of rate of increaseof pressure at which the movable switch 46 is actuated under suddenincreases in transformer oil. pressure can be varied. it is to be notedthat due to the above-described structure, the operating pin 69 of themovable switch 46 remains in contact with the end of the rod 56irrespective of the pressure of the oil 18 surrounding the bellows 44.

The reason that the switch operating rod 58 is able to effect anactuation of the movable switch 46 when sudden increases in thetransformer oil pressure occur is that the inertia of the unbalancedmass, which includes the movable switch 46, is greater than the switchoperating force needed to effect an actuation of the movable switch 46.On gradual increases in the transformer oil pressure, the switchoperating force, as effected by the switch operating rod 5, is not ofsufiicient magnitude to effect an actuation of the movable switch 46 andas a result, the movable .witch 46 is bodily moved until its furthermovement is prevented by the stop member 425. When further movement isprevented, the movable switch 4: 46 is actuated by the switch operatingrod 58, as will be explained more fully hereinafter.

In this instance, the movable switch 46, as illustrated in more detailin Fig. 3, is a microswitch and comprises a stationary contact member'70, a movable contact member 72 carried by a snap acting leaf spring 7dwhich in normal operation biases the movable contact member '72 to theopen position with respect to the stationary Contact member 76, and theoperating pin 69 which actuates the snap actin leaf spring 74 inresponse to the outward movement of the switch operating rod 56.

Referring again to the stop member 48, the stop member 43 comprises anL-shaped bracket 78, one end of which is suitably secured to the platemember 54, an adjustable screw fill carried by the bracket 78, and alock nut 32 provided to prevent movement of the adjustable screw 8t)with respect to the bracket '78 once the screw 86 has been properlyadjusted. The position of the end of the screw 39 with respect to themovable switch 46 determines at what total transformer oil pressure themovable switch 46 will be actuated. For instance, the closer the end ofthe screw 80 to the movable switch 46, the lower will be the pressure ofthe transformer oil 18 at which the movable switch 46 is actuated.

The operation of the apparatus illustrated in Fig. 1 will now bedescribed. Assuming the pressure of the transformer oil 18 suddenlyincreases, then a pressure wave front will strike the base member 52 ofthe Sylphon bellows 50, to thereby effect a movement of the switchoperating rod 58 to the left, as illustrated. When the switch operatingrod 58 is suddenly actuated to the left, it effects an actuation of theoperating pin 6% of the movable switch 46, to thereby effect a snapaction of the leaf spring 74, to thus bring the movable contact member72 into electrical contact with the stationary contact member 76.

When the movable contact member 72 of the movable switch 46 is inelectrical contact with the stationary contact member 70, an electricalcircuit is completed to the operating coil 32 of the trip mechanism 28.The energization of the operating coil 32 effects a movement of themagnetic core member 30 to the left, as illustrated, to thereby effectan opening of the circuit breaker 22, to thus deenergize the transformerlb. When the fault or other condition bringing about the sudden increasein the pres sure in the transformer oil 18 is relieved, the compressionspring 60 restores the Sylphon bellows to its normal position. Ofcourse, in order to reenergize the transformer 16, the handle 29 must beactuated upward to thereby close the circuit breaker 22.

Assuming the pressure of the transformer oil 18 gradually increases,then the switch operating rod 58 is gradually actuated towards the left,as illustrated. However, the force exerted on the operating pin 69 ofthe movable switch 46 is not of suflicient value to effect a snap actionof the leaf spring 74. Therefore, a bodily movement of the movableswitch 46 is effected which continues as the transformer oil pressuregradually increases until finally the movable switch 46 engages the endof the screw 86. When the movable switch 46 engages the end of the screw80, further movement of the switch 46 is prevented and thus, on furthermovement of the switch operating rod 58 to the left, the movable contactmember 72 is brought into electrical engagement with the stationarycontact member 70. When the contact members 76 and 72 are brought intoelectrical engagement, the transformer 10 is deenergized in the samemanner as hereinbefore described.

The apparatus embodying the teachings of the invention has severaladvantages. For instance, even though a pressure wave front effects aslight movement of the transformer tank wall associated with thepressure responsive device 20 still owing to the inertia of theunbalanced mass, which includes the movable switch 46, there issubstantially no movement of the switch 46.

Such being the case, the speed of response of the pressure responsivemeans 20 is maintained at a high value. In addition, the pressureresponsive means 20 comprises few components which can be readilymanufactured and assembled. Further, the pressure responsive means 20 isreadily adaptable to transformers of different power ratings.

Since certain changes may be made in the above described apparatus anddifferent embodiments of the invention may be made Without departingfrom the spirit and scope thereof, it is intended that all mattercontained in the foregoing description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

I claim as my invention:

1. In combination, a receptacle containing a fluid under pressure, anarm pivoted about a predetermined pivot point, a switch having operatingmeans for effecting an actuation of the switch, the switch being mountedon the pivoted arm for movement therewith, a mass also mounted on thepivoted arm for movement therewith, said mass being adjustable so thatits distance from the pivot point can be varied, pressure responsivemeans including an actuating member disposed to engage and effect anactuation of said switch operating means, said actauting member beingresponsive to the pressure of the fluid for actuating the switch inresponse to sudden changes in fluid pressure and for effecting bodilymovement of the pivoted arm and switch, without actuating the switch, inresponse to gradual changes in the fluid pressure, and means forlimiting the movement of the switch so that the said actuating membercan effect an actuation of the switch when the fluid pressure reaches apredetermined value.

2. in combination, a receptacle containing a fluid under pressure, anarm pivoted about a predetermined pivot point and having threads on theend thereof opposite the pivot point, a nut disposed on the threaded endof the pivoted arm, the nut being adjustable so that its distance fromthe pivot point can be varied, a switch having operating means foreffecting an actuation of the switch, the

switch being mounted on the pivoted arm for movement therewith, pressureresponsive means including an actuating member disposed to engage andeffect an actuation of said switch operating means, said actuatingmember being responsive to the pressure of the fluid for actuating theswitch in response to sudden changes in fluid pressure and for effectingbodily movement of the pivoted arm and switch, without actuating theswitch, in response to gradual changes in the fluid pressure, and meansfor limiting the movement of the switch so that the said actuatingmember can effect an actuation of the switch when the fluid pressurereaches a predetermined value.

3. In combination, a receptacle containing a fluid under pressure, anarm pivoted about a predetermined pivot point and having threads on theend thereof opposite the pivot point, a nut disposed on the threaded endof the pivoted arm, the nut being adjustable so that its distance fromthe pivot point can be varied, a switch having operating means foreflecting an actuation of the switch, the switch being mounted on thepivoted arm for movement therewith, pressure responsive means includinga Sylphon bellows having a base member and an actuating member carriedby the base member and disposed to engage and effect an actuation ofsaid switch operating means, said actuating member being responsive tothe pressure of the fluid for actuating the switch in response to suddenchanges in fluid pressure and for effecting bodily movement of thepivoted arm and switch, without actuating the switch, in response togradual changes in the fluid pressure, and means for limiting themovement of the switch so that the said actuating member can effect anactuation of the switch when the fluid pressure reaches a predeterminedvalue.

References Cited in the file of this patent UNITED STATES PATENTS2,094,319 Faust Sept. 28, 1937 2,357,878 Crew Sept. 12, 1944 2,648,741Starbird Aug. 11, 1953 2,658,122 Stein Nov. 3, 1953

